1. Place tongue in a large pot and fill with water to cover by a couple of inches. Boil for two to three hours, until fork-tender. Allow to cool slightly, and peel while still warm. When completely cooled, slice and place in an oven-safe pan for rewarming.
2. To make the pomegranate glaze: In a medium pot, bring pomegranate juice, sugar, and lemon juice to a boil. Reduce heat to low and cook for one hour, stirring occasionally.
3. In a small pot, sauté shallot in oil. When soft and translucent, add pomegranate juice mixture, vinegar, salt, and pepper. Bring to a boil, then remove from heat.
4. Pour pomegranate glaze over tongue, reserving a small amount for plating.
5. Toss cooked couscous with pomegranate arils and parsley. Stir together orange juice, oil, and vinegar and pour over couscous.